1. Technical Field
The present invention relates generally to a linear suspension element and, more particularly, to a linear suspension element for long-life reciprocation along a line of motion. The invention also relates to a reciprocator and linear suspension including the linear suspension element.
2. Related Art
There are a variety of linear suspensions available to constrain movement of a moving element in a linear motor or reciprocator. These suspensions are analogous to bearings in rotary devices because they restrict a moving element to primarily move in the operationally useful sense and prevent motion in other directions. Additional objectives of a linear suspension (as opposed to linear bearings) are to provide long-life reciprocation with no friction or wear.
U.S. Pat. No. 5,522,214 to Beckett et al. discloses an exemplary spiral suspension for a reciprocator. This suspension spirally expands to allow its center to move perpendicularly to the spiral plane. It resists radial movement to limit linear motion of a moving element to a single axis perpendicular to the spiral plane.
A problem with spiral suspensions is their inducement of a torsional motion about the reciprocation axis. This motion may cause vibration and failure and requires the moving element to be circular in section, or have excessive clearances to the stationary elements of an assembly in order not to collide with the stationary elements during operation. Accordingly, spiral suspensions are useless with xe2x80x9cSTARxe2x80x9d reciprocators in which the moving element and stationary elements mate in a generally non-circular manner. In xe2x80x9cSTARxe2x80x9d reciprocators, the suspension must exhibit substantial torsional stiffness as well as radial stiffness.
Strap suspensions, such as described incidentally in U.S. Pat. No. 5,389,844, have been developed for xe2x80x9cSTARxe2x80x9d reciprocators. In these suspensions, tensile stresses experienced by legs, or flexure elements, of the strap are transferred to bending stresses in the vertically mounted ends of the legs. A problem with these suspensions, however, is that users do not adequately monitor fretting that may occur on the ends of the flexure elements where they are clamped. Furthermore, the clamping of the legs to the mount is mechanically cumbersome.
In view of the foregoing there is a need in the art for a suspension element capable of withstanding operational and non-axial stresses and providing longer life. Further, there is a need for a reciprocator and suspension having the same characteristics.
The invention provides an improved linear suspension element and a reciprocator using the linear suspension element. The suspension element includes preloaded legs connecting a moving element to a static element of the reciprocator. The preloads substantially reduce fretting, simplify the mechanical coupling structure, provide longer life and maximize stroke within allowable stress limits.
A first aspect of the invention provides a linear suspension element for a moving element, the suspension element comprising: a mount; a plurality of preloaded legs each having a first portion for coupling to a moving element, and a second portion coupled to the mount.
A second aspect provides a reciprocator comprising: a linear drive mechanism for linearly moving a moving element; at least one linear suspension element operatively coupled to the linear drive mechanism, each linear suspension element having: a mount; a plurality of legs each having a first portion for coupling to a moving element, and a second portion coupled to the mount; and wherein each leg includes a preload.
The invention also includes, in a third aspect, a linear suspension for a moving element of a reciprocator having a linear drive mechanism for the moving element, the suspension comprising: a first mount coupled to the linear drive mechanism; a plurality of preloaded legs each having a first portion coupled to the moving element, and a second portion coupled to the first mount; a second mount coupled to the linear drive mechanism; and a plurality of preloaded legs each having a first portion coupled to the moving element, and a second portion coupled to the second mount.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.